square law RF detector - choice of diodes in commercial design

[[email protected]]

Below is the reverse engineered schematic of the famous BOONTON RF
MILLIVOLTMETER probe (also Ballantine labs). The unmarked diodes
*must* have a square law characteristic like germanium in order to
work down to a mere 50uV, but yet the thing works up into the GHz
region and has a mere 1.5pF input capacitance, indicating that they
are NOT a 1N34A.

+-------+-------+
| If | Vf |
+-------+-------+ Measured at
| 10uA 140mV | 20 degrees
| 100uA 210mV | Celcuis
| 1mA 320mV |
+---------------+

1/8W CF 1/4W CC
100 ohm 330 ohm
5% 10%
+---|<|----/\/\/----+----/\/\/-----> out -
| |
| diode ---
| 1nF --- Out to
| Cer | differential
<----||----+ +--------------> GND chopper type
| Cer | amplifier
1.5nF | 1nF --- and shaper
chip | diode ---
| |
+---|>|----/\/\/----+----/\/\/-----> out +
5% 10%
100 ohm 330 ohm
1/8W CC 1/4W CC

How would I find out what these unmarked diodes are? Most of the
boonton meters from eBay are without probes, and I would like to help
folks make their own probes by posting this info. Please see:

http://members.shaw.ca/novotill/MillivoltmeterRfProbe/index.htm

Thanks from Stepan

 

[Joerg]

Hello Stepan,

How would I find out what these unmarked diodes are? ...

You could carefully measure one but if you find out it's indeed GE then
you may not be able to source any. In the old days they did use GE point
contact diodes here but these were fickle (easily damaged on impact,
like a probe falling down) and they probably had to select the heck out
of them before binning them for production. Nowadays Schottky and GaAs
diodes are used. More reliable.

Here is an interesting paper about this stuff:
http://www.rohde-schwarz.com/www/download_files.nsf/file/SLMESS_E.PDF/$file/SLMESS_E.PDF

Regards, Joerg

 

[[email protected]]

Hi Joerg, From the link you gave:
-------------------------------
Today, zero bias Schottky diodes produced
on a silicon substrate or GaAs
diodes are being mostly used. Their
electrical characteristics are similar to
those of the germanium point-contact
diodes, but their long-term stability is
as high as that of thermocouples.
------------------------------

Hmm, I wonder where I can find datasheets for the above mentioned very
special diodes. Clearly no *ordinary* schottky or GaAs diode has a
usefull a square law curve at microvolt levels, like a germanium diode
does. Such data sheets elude me on google.

The boonton probe I referenced is '80s vintage and the direct
descendant of that probe being sold today by Boonton/Ballantine, has
the same specs and is compatible with the same meters, so it must not
be a germanium diode, even though my measurements at 10uA and 100uA
and 1mA at 20 degrees C do indicate germanium. I could measure the
reverse breakdown voltage too but I'm afraid to do that without a
datasheet. I have not measured thermal response. The probe runs
without dc bias to the diodes.

....Stepan

 

[[email protected]]

On Sun, 06 Nov 2005 04:10:59 GMT, [email protected] wrote:

I should clarify that it is the special GaAs diodes that I'm having
trouble finding the datasheets for.

....Stepan

 

[John Woodgate]

I read in sci.electronics.design that [email protected] wrote (in

Clearly no *ordinary* schottky or GaAs diode has a usefull a square law
curve at microvolt levels, like a germanium diode does.

Are you sure about that? I think the square law relates to the action of
the diode 'peak' detector *circuit* on an r.f. input, not to the d.c.
characteristics of the diode, which are exponential.

I've measured '+2 dB out for +1 dB in' on detectors using 1N4148s.

In that probe circuit, you do need 'matched' diodes. How to 'match'
them, though?

 

[[email protected]]

Are you sure about that? I think the square law relates to the action of
the diode 'peak' detector *circuit* on an r.f. input, not to the d.c.
characteristics of the diode, which are exponential.

I've measured '+2 dB out for +1 dB in' on detectors using 1N4148s.

In that probe circuit, you do need 'matched' diodes. How to 'match'
them, though?

Look at the graph comparing the germanium diode to the silicon diode:

http://engphys.mcmaster.ca/~elmer101/sqlaw/sqlaw.html

The slope of the V-I line is zero for silicon around the microvolt
level. I believe that means the signal is overcome by noise and
thermal drift so that you can't get a reliable reading.

....Stepan

 

[John Woodgate]

I read in sci.electronics.design that [email protected] wrote (in

Look at the graph comparing the germanium diode to the silicon diode:

http://engphys.mcmaster.ca/~elmer101/sqlaw/sqlaw.html

The slope of the V-I line is zero for silicon around the microvolt
level.

It only looks like zero because of the particular graph scales the
author chose.

I believe that means the signal is overcome by noise and thermal drift
so that you can't get a reliable reading.

You do need careful design, but it isn't impossible. Remember that on
the d.c. side you only need enough bandwidth to follow any changes you
are interested in, so it can be quite low, thus minimizing noise. Why
not take up the author's suggestion of a biased Schottky diode?

 

[The Phantom]

I read in sci.electronics.design that [email protected] wrote (in


Are you sure about that? I think the square law relates to the action of
the diode 'peak' detector *circuit* on an r.f. input, not to the d.c.
characteristics of the diode, which are exponential.

The ubiquitous 1N2x diodes were specifically designed to be square law
detectors: http://www.fairradio.com/1n21.htm

At least one of the Radiation Lab books discusses them.

 

[[email protected]]

The ubiquitous 1N2x diodes were specifically designed to be square law

detectors: http://www.fairradio.com/1n21.htm

At least one of the Radiation Lab books discusses them.

LOL the 1N21 is older than I am! But I think it's interesting and
usefull. I wonder if 1N21 derivative is what's in here:
http://members.shaw.ca/novotill/ChopperRadarDetector/index.htm
too bad it won't fit into the RF probe since I have a few.

And below is partial datasheet for the 1N21:

1N21... Point Contact Mixer Diodes.
from an ALPHA datasheet

Maximum Ratings:
Power Dissipation = 100mW
Derating above 25 grdC. : 8 mW/grdC.
Top = Tstg = -55 to 150 grdC.

Characteristics:
Frequency Range: 2 GHz to 4 GHz, S- Band
Test Frequency : 3.1 GHz
L.O.Power : 0.5 mW
Z if :
1N21C : min 300 Ohm, max 500 Ohm
1N21D : min 325 Ohm, max 425 Ohm
1N21E : min 350 Ohm, max 450 Ohm
1N21F : min 350 Ohm, max 450 Ohm
1N21G : min 350 Ohm, max 450 Ohm
VSWR :
1N21D : max 1.5
1N21E,F,G : max 1.3
Proof Burnout : 5 Ergs
Noise Figure at N?= 1.5 dB:
1N21C : max 8.3 dB
1N21D : max 7.3 dB
1N21E : max 7 dB
1N21F : max 6 dB
1N21G : max 5.5 dB

Suffix: R = Reverse, M = Matched Pair, W = Reversible
______________________________________
Without guaranty! Mistakes are possible. Please ask via email if you
find a strange value!

______________________________________


1N23... Point Contact Mixer Diodes.
from an ALPHA datasheet

Maximum Ratings:
Power Dissipation = 100mW
Derating above 25 grdC. : 8 mW/grdC.
Top = Tstg = -55 to 150 grdC.

Characteristics:
Frequency Range: 8 GHz to 12 GHz, X- Band
Test Frequency : 9.4 GHz
L.O.Power : 1 mW
Z if :
1N23D : min 350 Ohm, max 450 Ohm
1N23E : min 335 Ohm, max 475 Ohm
1N23F : min 335 Ohm, max 465 Ohm
1N23G : min 335 Ohm, max 465 Ohm
1N23H : min 335 Ohm, max 465 Ohm
VSWR : max 1.3
Proof Burnout : 2 Ergs
Noise Figure at N?= 1.5 dB (Index leider nicht lesbar):
1N23D : max 7.8 dB
1N23E : max 7.5 dB
1N23F : max 7 dB
1N23G : max 6.5 dB
1N23H : max 6 dB

Suffix: R = Reverse, M = Matched Pair, W = Reversible

______________________________________
Without guaranty! Mistakes are possible. Please ask via email if you
find a strange value!

______________________________________

 

[[email protected]]

I read in sci.electronics.design that [email protected] wrote (in


It only looks like zero because of the particular graph scales the
author chose.


You do need careful design, but it isn't impossible. Remember that on
the d.c. side you only need enough bandwidth to follow any changes you
are interested in, so it can be quite low, thus minimizing noise. Why
not take up the author's suggestion of a biased Schottky diode?

That's the million dollar question. Especially since the folks at
Boonton and at Ballantine Labs chose not to use external bias in their
industry-standard meters. I own the Boonton 9200A and it gives
readings down to 50uV without using any kind of bias.

I wonder if it's to keep the probe input capacitance or impedance
suffering. ???

....Stepan

 

[Chris Jones]

Below is the reverse engineered schematic of the famous BOONTON RF
MILLIVOLTMETER probe (also Ballantine labs). The unmarked diodes
*must* have a square law characteristic like germanium in order to
work down to a mere 50uV, but yet the thing works up into the GHz
region and has a mere 1.5pF input capacitance, indicating that they
are NOT a 1N34A.

+-------+-------+
| If | Vf |
+-------+-------+ Measured at
| 10uA 140mV | 20 degrees
| 100uA 210mV | Celcuis
| 1mA 320mV |
+---------------+

1/8W CF 1/4W CC
100 ohm 330 ohm
5% 10%
+---|<|----/\/\/----+----/\/\/-----> out -
| |
| diode ---
| 1nF --- Out to
| Cer | differential
<----||----+ +--------------> GND chopper type
| Cer | amplifier
1.5nF | 1nF --- and shaper
chip | diode ---
| |
+---|>|----/\/\/----+----/\/\/-----> out +
5% 10%
100 ohm 330 ohm
1/8W CC 1/4W CC

How would I find out what these unmarked diodes are? Most of the
boonton meters from eBay are without probes, and I would like to help
folks make their own probes by posting this info. Please see:

http://members.shaw.ca/novotill/MillivoltmeterRfProbe/index.htm

Thanks from Stepan

Look on the Agilent website for the HSMS-2852 or similar. I'd post a link,
but they made the URL about 200 characters long, and it probably contains
all the information they've gathered about me for the past 5 years...

There are lots of application notes on there too.

Chris

 

[Joerg]

Hello Stepan,

LOL the 1N21 is older than I am! But I think it's interesting and
usefull. I wonder if 1N21 derivative is what's in here:
http://members.shaw.ca/novotill/ChopperRadarDetector/index.htm
too bad it won't fit into the RF probe since I have a few.

Just wondering: If this one doesn't fit could the OA91 be similar? I had
used it a lot for detectors when I was young. It was in the skinny glass
housing, not the big one like many other OA diodes.

As to where to get GaAs diodes that may be tough in small quantities.
Ixys makes only the big ones IIRC and those will likely have too much
capacitance for you and be too large.

Regards, Joerg

 

[Joerg]

Hello Chris,

Look on the Agilent website for the HSMS-2852 or similar. I'd post a link,
but they made the URL about 200 characters long, and it probably contains
all the information they've gathered about me for the past 5 years...

Are they engaging in cookie-mania? This diode looks like a good deal at
89 cents. An interesting facet is how they write "optimised", in
rightpondian lingo. Did they buy this design from a company in the UK?

Regards, Joerg

 

[John Woodgate]

I read in sci.electronics.design that Chris Jones

Look on the Agilent website for the HSMS-2852 or similar. I'd post a
link, but they made the URL about 200 characters long, and it probably
contains all the information they've gathered about me for the past 5
years...

This URL is manageable:

http://cp.literature.agilent.com/litweb/pdf/5989-4022EN.pdf

 

[[email protected]]

On Sun, 6 Nov 2005 21:59:44 +0000, John Woodgate

Since this thread will live forever on Google,
here is a summary of detector diode possibilities
for use in RF millivoltmeter microwattmeter probes:

We note that these are used in RFID tags
and that we google the like shown below:
zero-bias schottky detector diode

We also note that there are many application
notes available and that we google for:
square-law detector schottky diode

Zero Bias Silicon Schottky Detectors:
www.agilent.com
HSMS-285x (looks good. Note Bv=3.8V)
http://www.micrometrics.com/
MZB600 (looks good. Note Bv=4V)
www.calmostech.com
CMS-825x.pdf (looks good. Note Bv=5V)
http://www.skyworksinc.com/
SMS7630 (looks good. Note Bv=3V)

Zero Bias GaAs Schottky Detector:
www.agilent.com
HSCH-9161 (works up to 100GHz !!!)

Low Barrier Schottky Detector:
www.infineon.com
BAT62 (Not great in microvolt range)

Old Germanium Point Contact
1N23 (fragile and large)
1N21 (fragile and large)
1N34A (high capacitive loading)
OA91 (high capacitive loading)

 

[[email protected]]

On Sun, 6 Nov 2005 21:59:44 +0000, John Woodgate

Since this thread will live forever on Google,
here is a summary of detector diode possibilities
for use in RF millivoltmeter microwattmeter probes:

We note that these are used in RFID tags
and that we google the like shown below:
zero-bias schottky detector diode

We also note that there are many application
notes available and that we google for:
square-law detector schottky diode

Zero Bias Silicon Schottky Detectors:
www.agilent.com
HSMS-285x (looks good. Note Bv=3.8V)
http://www.micrometrics.com/
MZB600 (looks good. Note Bv=4V)
www.calmostech.com
CMS-825x.pdf (looks good. Note Bv=5V)
http://www.skyworksinc.com/
SMS7630 (looks good. Note Bv=3V)

Zero Bias GaAs Schottky Detector:
www.agilent.com
HSCH-9161 (works up to 100GHz !!!)

Low Barrier Schottky Detector:
www.infineon.com
BAT62 (Not great in microvolt range)

Old Germanium Point Contact
1N23 (fragile and large)
1N21 (fragile and large)
1N34A (high capacitive loading)
OA91 (high capacitive loading)

You should look at HP AN 986 "Square Law and Linear Detection"
and HP AN 987 "Is Bias Current Necessary?"

But another thought would be:
Why not use comtemporary diodes and maybe improve the
performance of the probe?


Good luck,
Dave

 

[John Woodgate]

I read in sci.electronics.design that [email protected] wrote (in
<[email protected]>) about 'square
law RF detector - choice of diodes in commercial design', on Mon, 7 Nov
2005:

You should look at HP AN 986 "Square Law and Linear Detection" and HP
AN 987 "Is Bias Current Necessary?"

Are they on the web? The numbers are now used for some chipsets, so
Google gives 3 million wrong hits.

 

[John Popelish]

I read in sci.electronics.design that [email protected] wrote (in
<[email protected]>) about 'square
law RF detector - choice of diodes in commercial design', on Mon, 7 Nov
2005:



Are they on the web? The numbers are now used for some chipsets, so
Google gives 3 million wrong hits.

I searched for [AN 987 "Is Bias Current Necessary?"] and the first hit
was:
http://coursemain.ee.ukzn.ac.za/enel4msh2/pracs/DiodeData/an-987-schot5.pdf

 

[John Popelish]

I read in sci.electronics.design that [email protected] wrote (in
<[email protected]>) about 'square
law RF detector - choice of diodes in commercial design', on Mon, 7 Nov
2005:



Are they on the web? The numbers are now used for some chipsets, so
Google gives 3 million wrong hits.

Try searching for [986 "Square Law and Linear Detection"].

 

[John Woodgate]

I read in sci.electronics.design that John Popelish <[email protected]>
wrote (in <[email protected]>) about 'square
law RF detector - choice of diodes in commercial design', on Mon, 7 Nov
2005:

I read in sci.electronics.design that [email protected] wrote (in
<[email protected]>) about 'square
law RF detector - choice of diodes in commercial design', on Mon, 7
Nov 2005:

Are they on the web? The numbers are now used for some chipsets, so
Google gives 3 million wrong hits.

I searched for [AN 987 "Is Bias Current Necessary?"] and the first hit
was:
http://coursemain.ee.ukzn.ac.za/enel4msh2/pracs/DiodeData/an-987-schot5.pdf

Thank you. The AN 986 is there as well, and can be downloaded, but the
DiodeData directory is not accessible. Not very sensible.